SINGAPORE - Moderna's Spikevax Covid-19 vaccine has been approved for use in 75 countries, with supply contracts for 1.7 billion doses already signed with the United States, Japan, China, Britain and the European Union, besides the global Covax vaccine-sharing facility.

Going forward, however, demand for Moderna's shots could be dampened, following Swedish health authorities' findings of an increased risk of inflammation of the heart muscle (myocarditis) and inflammation of the lining outside the heart (pericarditis) among youth and young adults who have been inoculated with the mRNA vaccine.

According to the Swedish Public Health Agency, the risk seemed especially tied to the second dose of the Moderna vaccine and was more prevalent among young men and boys, in the weeks just following the second jab.

The cardiovascular side effects usually resolve by themselves, but those affected should be evaluated by a doctor, the agency added.

The risk of side effects after vaccination is not unique to Moderna's vaccine. Pfizer-BioNTech's Covid-19 vaccine has also been found to cause inflammation of the heart muscle or the lining outside the heart.

However, the risk of health complications due to Moderna's shots, while still small, was found to be greater than that of the Pfizer-BioNTech vaccine.

Thus far, Sweden and Denmark are the only countries that have paused the use of Moderna's Covid-19 vaccine for younger age groups over the possible health complications.

About 81,000 people in the concerned age group under 30 had already received a first Moderna jab in Sweden, but they will not be offered a second. The temporary suspension will be in force till Dec 1 until a review is conducted.

In Denmark, Moderna shots have been suspended for people younger than 18.

Norway had already been recommending Pfizer-BioNTech's Cominarty vaccine for minors and reiterated that advice on Wednesday.

Finland on Thursday (Oct 7) announced its own decision to halt the vaccination of minors with Moderna's Spikeva.

On Oct 1, Canadian health officials had highlighted data which suggested that the risk of heart inflammation was higher after Moderna jabs, compared with Pfizer-BioNTech shots. That could be a precursor to limiting its use for minors and young adults in the North American country.